Add linear query matcher

lib/n_plus_one_control/rspec.rb

@@ -5,6 +5,7 @@
 require "n_plus_one_control"
 require "n_plus_one_control/rspec/dsl"
 require "n_plus_one_control/rspec/matchers/perform_constant_number_of_queries"
+require "n_plus_one_control/rspec/matchers/perform_linear_number_of_queries"
 require "n_plus_one_control/rspec/context"
 
 module NPlusOneControl

lib/n_plus_one_control/rspec/matchers/perform_linear_number_of_queries.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+# rubocop:disable  Metrics/BlockLength
+::RSpec::Matchers.define :perform_linear_number_of_queries do |slope: 1, intercept: 1|
+  supports_block_expectations
+
+  match do |actual, *_args|
+    raise ArgumentError, "Block is required" unless actual.is_a? Proc
+
+    raise "Missing tag :n_plus_one" unless
+      @matcher_execution_context.respond_to?(:n_plus_one_populate)
+
+    populate = @matcher_execution_context.n_plus_one_populate
+
+    @matcher_execution_context.executor = NPlusOneControl::Executor.new(
+      population: populate,
+      matching: nil,
+      scale_factors: @factors
+    )
+
+    @queries = @matcher_execution_context.executor.call(&actual)
+
+    @queries.all? do |scale, queries|
+      queries.size <= slope * scale + intercept
+    end
+  end
+
+  match_when_negated do |_actual|
+    raise "This matcher doesn't support negation"
+  end
+
+  # TODO: failure message for linear queries
+  # failure_message { |_actual| NPlusOneControl.failure_message(@queries) }
+end
+# rubocop:enable  Metrics/BlockLength

spec/n_plus_one_control/rspec/matchers/perform_constant_number_of_queries_spec.rb

@@ -52,7 +52,7 @@
       expect do
         expect { Post.find_each { |p| p.user.name } }
           .to perform_constant_number_of_queries
-      end.to raise_error(RSpec::Expectations::ExpectationNotMetError, /select .+ from.*↳ .*rspec_spec.rb:\d+/im)
+      end.to raise_error(RSpec::Expectations::ExpectationNotMetError, /select .+ from.*↳ .*_spec.rb:\d+/im)
     end
 
     context "when truncate size is specified" do
@@ -87,7 +87,7 @@
             .to perform_constant_number_of_queries
         end.to raise_error(
           RSpec::Expectations::ExpectationNotMetError,
-          /select .+ from.*↳.*rspec_spec.rb:\d+.*\n.*rspec_spec.rb:\d+/im
+          /select .+ from.*↳.*_spec.rb:\d+.*\n.*_spec.rb:\d+/im
         )
       end
     end

spec/n_plus_one_control/rspec/matchers/perform_linear_number_of_queries_spec.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe NPlusOneControl::RSpec do
+  describe 'perform_linear_number_of_queries' do
+    context "when constant queries", :n_plus_one do
+      populate { |n| create_list(:post, n) }
+
+      specify do
+        expect { Post.preload(:user).find_each { |p| p.user.name } }
+          .not_to raise_error(RSpec::Expectations::ExpectationNotMetError)
+      end
+    end
+
+    context "when has linear query", :n_plus_one do
+      populate { |n| create_list(:post, n) }
+
+      specify do
+        expect { Post.find_each { |p| p.user.name } }
+          .to perform_linear_number_of_queries
+      end
+    end
+
+    context "when has linear query larger than expected slope", :n_plus_one do
+      populate { |n| create_list(:post, n) }
+
+      specify do
+        expect do
+          expect { Post.find_each { |p| "#{p.user.name} #{p.category.name}" } }
+            .to perform_linear_number_of_queries
+        end.to raise_error(RSpec::Expectations::ExpectationNotMetError)
+      end
+    end
+
+    context "when context is missing" do
+      specify do
+        expect do
+          expect { subject }.to perform_linear_number_of_queries
+        end.to raise_error(/missing tag/i)
+      end
+    end
+
+    context "when negated" do
+      specify do
+        expect do
+          expect { subject }.not_to perform_linear_number_of_queries
+        end.to raise_error(/support negation/i)
+      end
+    end
+  end
+end

spec/support/category.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+ActiveRecord::Schema.define do
+  create_table :categories do |t|
+    t.string :name
+  end
+end
+
+class Category < ActiveRecord::Base
+  has_many :posts
+end
+
+FactoryGirl.define do
+  factory :category do
+    name "Category"
+  end
+end

spec/support/post.rb

@@ -4,16 +4,19 @@
   create_table :posts do |t|
     t.string :title
     t.integer :user_id
+    t.integer :category_id
   end
 end
 
 class Post < ActiveRecord::Base
   belongs_to :user
+  belongs_to :category
 end
 
 FactoryGirl.define do
   factory :post do
     title "Title"
     user
+    category
   end
 end